1. Field of the Invention
The present invention relates to a display device using pixels in shapes of rotating cylinder, etc. More specifically, the present invention relates to a display device in which a plate-shaped or a cylinder-shaped pixels having a half part that is colored and having, on the surface, an organic molecular film carrying positive and negative charges to generate a dipole moment are dipped in liquid; the pixels dipped in liquid are disposed between electrodes and at least one of the electrodes located in a path in which light passes is transparent; and voltage is applied to the electrodes so as to rotate the pixels.
2. Description of the Prior Art
A display device using pixels in shapes of a rotating ball or a rotating cylinder has been proposed as a twist ball display by N. K. Sheridon et al. in 1977 (Proceeding of the SDI, vol. 18/3 & 4, p289, 1977). In such a display device, minute balls, each having a colored half surface, are sandwiched between counter electrodes, one of which is transparent, arranged in a two-dimensional matrix, and the minute balls are present in a liquid electrolyte. One half surface of the minute balls has a surface charge which has an opposite polarity to the those of another half surface. Thus, the minute balls have a dipole moment as a whole. At this time, when voltage is applied to one of the portions between the counter electrodes, the minute balls are rotated by an electric field in the direction in which the direction of the dipole moment is the same as the direction of the electric field. Therefore, by applying a predetermined voltage to each counter electrode, each minute ball is rotated in accordance with the applied voltage and functions as a pixel.
In a conventional display, in order to provide the surface of the minute balls with charge, a half surface of the balls including titanium oxide was coated with a chalcogen-based inorganic material, etc. by a vacuum deposition method, etc. Since each material has a predetermined zeta potential in the liquid electrolyte, respectively, by appropriately selecting a coating material, the balls were provided with dipole moments and were able to be used as pixels.
However, in general, inorganic materials are required to be exposed to a strongly alkaline or strongly acid solution to increase the surface charge density. However, it is not preferable to use such a solution since there is a problem from a view of the safety, that is, the requirements for the apparatus for housing a solution.
Furthermore, in order to provide the ball with a large dipole moment, a coating material for coloring was limited, thus limiting the colors to be used for coloring a display. For such reasons, the dipole moment of the minute ball used for the twist ball display was small. Therefore, in order to rotate the minute ball, it was necessary to add an electric field as large as several kilo volt/cm (Maski Saito, “Journal of the Imaging Society of Japan” vol. 38, No. 2, p 143 in 1999).
Furthermore, in order to realize the twist ball display, various manufacturing methods have been proposed, for example, by thinly coating the surfaces of the minute balls with resin; allowing them to be trapped in a plate of hydrous polyvinyl alcohol resin and then evaporating a moisture component for solidification. Thereafter, the plate is impregnated with an organic solvent to dissolve the resin on the surface of the minute ball, thereby forming a gap between the ball surface and the polyvinyl alcohol resin plate. Thereafter, this plate is sandwiched between the glass substrates and fill liquid between the substrates. In this method, the plate of the polyvinyl alcohol resin absorbs the liquid, and as a result, the gap between the ball and the plate is filled with the liquid.
However, in the above-mentioned manufacturing method, it takes much time and effort to coat the minute balls with resin, and furthermore, it is difficult to control the distributed density of the minute balls in the resin with high accuracy. Furthermore, since the plate material is sandwiched between the glass substrates, there is a limitation on reducing a space between the electrodes. Thus, it is difficult to increase an electric field applied to the minute balls. As a result, the rotation speed of the minute balls becomes small, reducing the response speed of images.
Furthermore, if materials have largely different refractive indexes, reflection occurs on the interface between the materials and a double image, etc. occurs, which may lead to an inferior viewability of images.